Multiple-frequency laser apparatus and method

Claim 3

A method as claimed in claim 1 and in which the stress is varied in at least one of direction, magnitude and time to alter the extent to which the multi-valley degeneracy is lifted, thereby to change the frequency separation associated with the various valleys.

Claim 4

A method as claimed in claim 1 and in which the strain is a symmetry-breaking stress.

Claim 5

A method as claimed in claim 1 and in which the population inversion is achieved by operating the semiconductor as a diode, the optical cavity being located in the vicinity of the junction region of the diode.

Claim 6

A method as claimed in claim 1 and in which the electron population inversion is effected by optical pumping.

Claim 7

A method as claimed in claim 5 and in which the semiconductor is axially optically pumped and the laser beam is emitted in a direction orthogonal to the direction of pumping.

Claim 8

A method as claimed in claim 1 and in which the electron population inversion is effected by passing an electron beam through the optical resonant cavity, energy being extracted from the beam to create negative electron temperature within the semiconductor.

Claim 9

A method as claimed in claim 1 and in which the stress applied is a shear stress.

Claim 10

A method as claimed in claim 8 and in which the stress is changed in time to effect frequency modulation of the laser beam.

Claim 11

A method as claimed in claim 1 and in which the frequencies of the multiple-frequency laser beam are mixed within the semiconductor to produce sum and difference and other combination frequencies in the laser output of the frequencies associated with the different energy gaps produced by the stress.

Claim 12

Apparatus for providing a multiple-frequency laser beam, that comprises, a multi-valley semiconductor forming at least part of an optical resonant cavity, means for establishing an inverted population in the occupation of the energy levels of the semiconductor, means for maintaining the lattice temperature of the semiconductor at a value low enough to enable the semiconductor material to sustain at least two separate inverted electron populations, the electron energy level population associated with each valley being substantially independent of the energy level populations of the other vallEys, means for applying a stress to the semiconductor, the stress being one that lifts the multi-valley degeneracy thereby producing different-valued energy gaps within the semiconductor material.

Claim 13

Apparatus for providing a multiple-frequency laser beam, that comprises, a multi-valley semiconductor forming at least part of an optical resonant cavity, means for establishing an inverted population in the occupation of the energy levels of the semiconductor, means for maintaining the lattice temperature of the semiconductor at a value low enough to enable the semiconductor material to sustain at least two separate inverted electron populations, the electron energy level population associated with each valley being substantially independent of the energy level populations of the other vallEys, means for applying a stress to the semiconductor, the stress being one that lifts the multi-valley degeneracy thereby producing different-valued energy gaps within the semiconductor material.

Claim 14

Apparatus as claimed in claim 11 and in which the optical resonant cavity is wholely within the semiconductor and has reflective faces that are parallel and planar to provide reflection surfaces to enable establishment of the laser beam.

Claim 15

Apparatus as claimed in claim 12 and in which the semiconductor is selected from the semiconductor group consisting of lead telluride, lead sulphide and lead selenide.

Claim 16

Apparatus as claimed in claim 12 and in which external mirrors at least form part of the optical resonant cavity.

Claim 17

Apparatus as claimed in claim 11 and in which means is provided external of the semiconductor for receiving the multiple-frequency beam and mixing the frequencies to provide sum and difference outputs.

Claim 18

Apparatus as claimed in claim 11 in which means is provided for modulating one of the frequencies, the multiple-frequency laser beam being transmitted to some remote region, means being provided at the remote region to receive the beam and to mix the modulated frequency with an unmodulated frequency thereby to create sum and difference signals.

Claim 19

Apparatus as claimed in claim 16 and in which demodulating means is provided to remove the modulating signal from the sum and difference signals.

Claim 20

Apparatus for providing a double-frequency laser beam that comprises in combination, a multi-valley semiconductor having an optical cavity, means for establishing an inverted population in the occupation of the energy levels of the semiconductor, means for maintaining the lattice temperature of the semiconductor at the value low enough to enable the semiconductor material to sustain two separate non-communicating inverted populations so that the energy level population associated with each valley is entirely independent of the energy level population of the other valley, and means for applying a stress to the semiconductor, the stress being one that lifts the multi-valley degeneracy thereby producing different-valued energy gaps within the material, means being provided to bias the semiconductor material periodically to remove the non-communicating character of the inverted populations thereby to create an optical flip-flop.

Claim 21

Apparatus for providing a double-frequency laser beam that comprises in combination, a multi-valley semiconductor having an optical cavity, means for establishing an inverted population in the occupation of the energy levels of the semiconductor, means for maintaining the lattice temperature of the semiconductor at the value low enough to enable the semiconductor material to sustain two separate non-communicating inverted populations so that the energy level population associated with each valley is entirely independent of the energy level population of the other valley, and means for applying a stress to the semiconductor, the stress being one that lifts the multi-valley degeneracy thereby producing different-valued energy gaps within the material, means being provided to bias the semiconductor material periodically to remove the non-communicating character of the inverted populations thereby to create an optical flip-flop.

Claim 22

Apparatus as claimed in claim 18 and in which the bias means comprises means for applying a symmetry stress sufficient to remove the non-communicating character of said semiconductor.

Claim 23

Apparatus as claimed in claim 18 and in which the bias means comprises means for applying a strong electric field to the semiconductor.

Claim 24

Apparatus for providing a multiple-frequency laser beam, that comprises, a multi-valley semiconductor forming at least part of an optical resonant cavity, the semiconductor being adapted to receive energy to establish an inverted population in the occupation of the energy levels therein, the electron energy level population associated with each valley being substantially independent of the energy level populations of the other valleys, and means for applying a symmetry-breaking stress to the semiconductor, the stress being one that lifts the multi-valley degeneracy and produces different-valued energy gaps within the semiconductor material.

Claim 25

Apparatus for providing a multiple-frequency laser beam, that comprises, a multi-valley semiconductor forming at least part of an optical resonant cavity, the semiconductor being adapted to receive energy to establish an inverted population in the occupation of the energy levels therein, the electron energy level population associated with each valley being substantially independent of the energy level populations of the other valleys, and means for applying a symmetry-breaking stress to the semiconductor, the stress being one that lifts the multi-valley degeneracy and produces different-valued energy gaps within the semiconductor material.

Claim 28

A method as claimed in claim 22 that comprises increasing the symmetry-breaking stress sufficiently so that the energy separation of the stress split conduction and/or valence band valleys will be large enough so that carriers can transfer from a high lying valley to a lower lying valley by emission of phonons with conservation of energy and momentum, the frequency of said phonons being determined by the stress.

Claim 29

A method as claimed in claim 23 in which the symmetry-breaking stress is amplitude modulated to effect creation and termination of said phonons and/or to frequency modulate said phonons.

Claim 30

A method as claimed in claim 22 that comprises varying said stress in at least one of direction, magnitude and time thereby to modulate the energy gaps provided in said active part and thereby vary the difference frequency between the multiple frequencies produced in said active part.

Claim 31

A method as claimed in claim 22 in which the applied symmetry-breaking stress is either mechanical, electrical or magnetic or a combination thereof.

Claim 32

A method as claimed in claim 22 that includes the further step of varying said symmetry-breaking stress with time to effect frequency modulation of said radiation, the wavelength of the modulating signal being long enough to subject substantially the whole active lasing region, at the same instant of time, to either compression or rarefaction by virtue of said varying stress.

Claim 33

A method as claimed in claim 22 that includes the further step of varying the stress upon the semiconductor with time to effect frequency modulation of said radiation, the changes in stress to effect such modulation being small compared to the symmetry-breaking stress applied to lift the multi-valley degeneracy.